The invention relates to devices for measuring pressure in liquids and gases and, in particular, to a semiconductor pressure sensing device.
The disclosed semiconductor pressure sensing device can be employed to measure pressure in drill holes and pipelines, in hydraulic and pneumatic aircraft systems, in internal combustion engines, in hydraulic agricultural mechanisms, as well as to measure superhigh pressures in laboratory conditions.
The present invention can be, besides, used for measuring the force in weighing heavy loads (railway cars, mine cars), as well as in forge and pressing equipment to control operational efforts.
There is known an effect of resistance changes in semiconductor materials in response to a hydrostatic pressure of the environment: air, gas, liquid.
This phenomenon is also known and employed to manufacture pressure gauges and, particularly, there is known a semiconductor pressure sensing device based on the n-type monocrystalline gallium antimonide, which is provided with two contacts and changes of the difference in signals between these contacts serves as an indication of the variation of the pressure.
The gallium antimonide conduction band possesses two minimums which relative energy location changes in response to the hydrostatic pressure, which results in the change of the electrical resistance of the pressure sensing device.
But the minimums of the conduction band in gallium antimonide move in response to pressure in one direction along the energy scale and the sensitivity coefficient of the gauge to pressure is low (less than 10.sup.-4 bar.sup.-1), the operational pressure range of such gauges based on gallium antimonide being limited to a range of from 0 to 10,000 bars.
The temperature stability of these gauges is insufficient: the temperature factor of sensitivity variation is too high and reaches 0.5% . deg.sup.-1.
There is known another pressure gauge comprising a solid based on AB.sub.1-x C.sub.x solid solution, composed of two semiconductor materials AB and AC of which the first has a direct forbidden band and the second has an indirect forbidden band and each of these materials has direct and indirect minimums of the conduction band, whereas the value of x which is the mole fraction of the AC material in the AB.sub.1-x C.sub.x solid solution is selected so as to bring close the energy of the direct and indirect minimums of the conduction band of the AB.sub.1-x C.sub.x solid solution. The pressure gauge also comprises a means for measuring changes in electric resistance of the solid in response to the applied pressure, which is electrically coupled to the solid.
The known pressure gauge is made on the basis of the GaAs.sub.1-x P.sub.x solid solution comprising gallium arsenide and gallium phosphide in a specified mole ratio.
The value of x in the GaAs.sub.1-x P.sub.x solid solution is selected depending on the range of pressures to be measured.
It is possible to produce gauges for measuring high or low pressures within a range of from 0 to 60,000 bars by selecting solid solutions with different values of x.
Sensitivity of such gauges to pressure is higher as compared to the monocrystalline gallium antimonide based gauges and lies within a range of from 2.00.sup.-4 to 4.10.sup.-4 bar.sup.-1 throughout the pressure range.
This can be accounted for by the fact that the minimums of the conduction band move in response to pressure in opposite directions of the energy scale.
However, a serious drawback of the known pressure gauge consists in the low temperature stability of its parameters, which is due to the change of the ratio between the thermal energy of the electron and the energy gap between the minima of the conduction band for the GaAS.sub.1-x P.sub.x solid solution.
Thus, according to the cited exterimental data on the dependence of the sensitivity factor upon the x value ratio for three temperatures +25.degree. C., -27.degree. C. and +90.degree. C. the sensitivity to pressure of the gauge based on the GaAs.sub.0.65 P.sub.0.35 solid solution changes by nearly 20% from 3.10.sup.-4 bar.sup.-4 at -27.degree. C. to 2.5.10.sup.-4 bars.sup.-1 at +90.degree. C., that is the temperature factor of sensitivity variation reaches almost 0.15% deg..sup.-1, which is a considerably large figure. For the pressure gauge based on the GaAs.sub.0.6 P.sub.0.4 sensitivity to pressure changes from 3.6.10.sup.-4 bar.sup.-1 at +25.degree. C. to 2.10.sup.-4 bar.sup.-1 at +90.degree. C., that is the temperature factor of sensitivity variation is equal to 0.7% . deg..sup.-1.
This significantly limits technical employment of such pressure gauges when the difference in the measured temperature varies widely.